A method for microwave-assisted catalytic hydrogenolysis of C-O bridge cleavage in coal-based platform molecules

Abstract

The application discloses a method for breaking C-O bridge bonds in coal-based platform molecules by microwave-assisted catalytic hydrogenolysis, and adopts active carbon loaded metal as a catalyst to hydrogenolyze coal-based platform molecule compounds under microwave-assisted heating, and adds solid acid in the reaction, so that the method and application for preparing fuel and fine chemicals by catalytic hydrogenolysis of coal-based platform molecule compounds are realized under normal pressure and temperature conditions. In the reaction process, microwave heating has the advantages of fast and uniform heating speed, high energy efficiency, easy operation control and the like, wherein the active carbon carrier can absorb microwaves and rapidly heat up, the existence of the metal can cause high hotspot temperature, and the solid acid can accelerate the reaction speed and control the product selectivity, through the action of giving protons or accepting electron pairs to the reactants, so that active carbon cation intermediate compounds are formed, the breaking of C-O bridge bonds in coal-based platform molecules is promoted, and then the coal-based platform molecules are decomposed into target products. The reaction process is environmentally friendly, raw material utilization rate is high, and has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of coal chemical industry, and relates to a method for breaking C-O bridge bonds in coal-based platform molecules by microwave-assisted catalytic hydrogenolysis, more specifically, a method for breaking C-O bridge bonds in platform molecules under mild conditions to prepare fuels and fine chemicals by microwave-assisted catalytic hydrogenolysis of coal-based platform molecules under the action of an activated carbon-supported metal catalyst and a solid acid and application thereof. BACKGROUND

[0002] Under the background of the "double carbon" target, it is urgent to improve the comprehensive utilization efficiency of coal as a chemical raw material and promote the high-end, diversification and low-carbon development of the coal chemical industry. Giving full play to the natural aromatic ring structure characteristics of coal, developing a technology for preparing high-end fine chemicals by coal directional cracking under mild conditions as a new way of non-energy utilization of coal can avoid the problem of homogenization of coal chemical and petroleum chemical product chains, improve the added value of coal-based products, and help the healthy and sustainable development of the coal chemical industry. The macromolecular structure of coal is a three-dimensional network structure connected by various bridge bonds (such as methine bond, ethylene bond, ether bond, thioether bond, methine ether bond and aromatic ring carbon-carbon bond, etc.), so high-value-added products can be obtained by catalytic hydrogenolysis of bridge bonds.

[0003] Japan developed a new NEDOL bituminous coal liquefaction cracking method based on the EDS process. The reaction temperature of this process is 465 DEG C, the reaction pressure is 19 MPa, the catalyst is synthetic iron sulfide or natural pyrite, and the solid-liquid separation uses the method of vacuum distillation. This catalytic reaction is carried out in a high-temperature and high-pressure environment, the reaction conditions are harsh, the energy consumption is large, and the economic effect is low (Journal of Japan Institute of Energy, 1993, 72(10):935-942).

[0004] Chinese patent CN114570420B reports a catalytic cracking catalyst and its preparation method and application. This method promotes the cracking reaction of macromolecular hydrocarbon compounds at high temperature and high pressure, thereby improving the selectivity of cracking products ethylene and propylene. This reaction method is harsh for the reaction device and is not easy to realize industrialization, and the consumption of catalyst is large, increasing the cost.

[0005] Chinese patent CN116676099A provides a fractionating device, method and use in a catalytic cracking or catalytic cracking process. The fractionating device includes a fractionating column, a feed unit, a column bottom oil unit and a back-refined oil unit. The feed unit includes a reaction oil gas feed pipeline and a fresh raw material feed pipeline. This reaction device is complex and expensive.

[0006] It is the only way for the scientific development of China's coal industry to obtain high value-added products by the conversion of bridge bonds in the molecular structure of coal under mild conditions and to greatly improve the economic benefits of coal conversion. C-O bridge bond is one of the main bridge bonds in coal molecules, and it is of great significance to study the catalytic hydrogenolysis under mild conditions to realize the cleavage of C-O bridge bond in coal-based platform molecules. Heating mode is an important factor affecting the process of catalytic hydrogenolysis reaction. At present, the main heating methods include traditional heating method and microwave-assisted heating method. The traditional heating method is to heat according to the principles of heat conduction and heat transfer, among which the electric heating method is the most common in catalytic cracking research. The fixed bed reactor and high temperature and high pressure reaction kettle involved in the reported literature are all heated by electricity. These reactors need to withstand high temperature and high pressure, and the material requirements for the device are high (Chemical Engineering Science, 2022, 253, 117554; Fuel Processing Technology, 2023, 242, 107647). Moreover, using the traditional heating method, heat is transferred from the heating medium to the sample surface, and then from the surface to the sample interior. In the whole heating process, there is a heat transfer resistance, which leads to heat loss and uneven heat distribution of the heated sample.

[0007] Chinese patent CN110368972A provides a core-shell SiC@C catalyst for microwave-assisted catalytic depolymerization of solid waste; SiC is used as a microwave absorbing medium. However, the preparation of SiC requires calcination of the precursor under N2 and steam atmosphere to obtain the core-shell SiC@C catalyst carrier, which requires heating to 500-650℃ and holding for 4-6h. The preparation conditions of such wave-absorbing materials require extremely high temperature, and the reaction time is relatively long, which is not conducive to reducing energy consumption.

[0008] Chinese patent CN114870875A places silicon source, foamed nickel, and carbon fiber sheet deposited with carbon layer by layer into a graphite stockyard, with carbon felt separating between layers; then places the graphite crucible into a high-temperature tube furnace for calcination, reacts at 1200℃ for 2h to obtain Cf / SiC / Ni composite material. The Cf / SiC / Ni composite material degrades methylene blue under a certain power of microwave. However, with the extension of hydrothermal reaction time, the thickness of the deposited carbon layer gradually increases, the diameter of the silicon carbide nanowires gradually increases, and the diameter of the nickel particles gradually increases, which reduces the degradation effect of methylene blue and the stability of the catalyst.

[0009] Chinese patent CN116688984A invention relates to a microwave-assisted process for catalytic cracking of polyethylene based on double-layer iron-based catalyst. The preparation of FeMO / CNT composite catalyst (M is one of Ni, Al, Co, Mn, Cu, Mg, Zn, Ce, Pd, Yb, La, Zr or a mixture of two) is prepared under microwave-assisted catalytic cracking of polyethylene. The polyethylene is mixed uniformly with the FeMO / CNT composite catalyst at the bottom of the reactor to form the first layer of material, and then the second layer of material FeMO / CNT composite catalyst is added on top of the first layer of material. After purging with nitrogen to exhaust the air, the microwave cracking reaction is carried out using the method of gradually increasing the microwave power. The overall process of this reaction is complex, and the microwave cracking uses a power as high as 1000W.

[0010] Unlike the heating principle of traditional heating methods, microwave is a form of energy, not heat, and microwave heating is achieved through a class of substances that can absorb microwaves and convert microwaves into heat. This class of substances is called microwave absorber. Compared with SiC, activated carbon is easier to prepare and is widely used as a microwave absorber, which can quickly raise the reaction to the target temperature under microwave heating. Fast and uniform heating, energy saving and efficient, easy to operate and control, which are the advantages of microwave-assisted heating method.

[0011] In addition, acidic catalysts can promote the breaking of bridge bonds in coal structure at much lower temperatures than coal pyrolysis reactions, effectively remove heteroatoms in coal, and significantly improve the yield of liquefied oil. Therefore, acidic catalysts have attracted the attention of many researchers. Common solid acid catalysts include acidic clay, alumina, zirconium sulfate, and zeolite molecular sieve, etc. However, most of the acidic carriers lose a large number of acid sites in the harsh environment of aqueous phase reaction, resulting in a decrease in catalytic performance and low reaction efficiency.

[0012] Chinese patent CN113559921B relates to a method for applying a metal-loaded mesoporous carbon-ZSM-5 microporous molecular sieve shell-core catalyst to microwave field biomass catalytic pyrolysis for oil production, but ZSM-5 microporous molecular sieve as a solid acid catalyst has low activity and weak pyrolysis ability, resulting in low carbon yield of the product (only 44.0%) and long reaction time.

[0013] Therefore, it is a difficult point in the current research to develop a method that overcomes the disadvantages of traditional heating methods and simultaneously catalytically cracks the bridge bonds connecting the basic structural units in the molecular structure of coal under normal pressure and temperature conditions. This method has great economic effect and industrial application value. SUMMARY

[0014] The application aims to overcome the disadvantages in the conventional heating catalytic reaction process, such as the heat transfer resistance existing in the heating process, resulting in heat loss, and the inevitable temperature gradient of the sample, and provide a method and application for hydrogenolysis of coal platform molecules under the condition of normal pressure microwave-assisted heating, so as to realize the preparation of fuels and fine chemicals by hydrogenolysis of coal.

[0015] The technical scheme of the application is as follows:

[0016] A method for microwave-assisted catalytic hydrogenolysis of C-O bridge bond in coal-based platform molecules, the steps are as follows:

[0017] Taking coal-based platform molecules as raw materials, isopropyl alcohol as a solvent, using Ru-Pd / AC catalyst as a hydrogenolysis catalyst, adding solid acid, introducing reaction gas hydrogen and controlling the flow rate to be 50ml / min, setting the microwave output power to be 500-900W, and the reaction time to be 20-60min, the C-O bridge bond in the coal platform molecules is selected for catalytic hydrogenolysis in the microwave reactor to generate aromatic compounds.

[0018] The Ru-Pd / AC catalyst has a metal Ru loading of 0wt.%-5wt.% and a metal Pd loading of 0wt.%-5wt.%, and the mass ratio of the Ru-Pd / AC catalyst to the coal-based platform molecules is 1:1-1:10.

[0019] The coal-based platform molecules are one of phenylbenzyl ether, dibenzyl ether, diphenyl ether and phenoxyethylbenzene, and the concentration of the coal-based platform molecules in the reaction system is 1%-20%.

[0020] The solid acid is one of phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid, and the mass ratio of the solid acid to the Ru-Pd / AC catalyst is not more than 3.

[0021] The aromatic compound is toluene, ethylbenzene, phenol, etc.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] (1) The solid acid is used in the catalytic hydrogenolysis reaction to accelerate the reaction speed and control the product selectivity, and the main activation mode is that the catalyst and the organic reactant molecules form a reactive carbon cation intermediate compound by giving protons or accepting electron pairs to the reactants, so as to promote the C-O bridge bond in the coal-based platform molecules to be broken, and then the catalyst process is promoted to decompose into products.

[0024] (2) The present application is carried out in a microwave reaction, and the microwave-assisted heating method has the advantages of fast and uniform heating speed, energy saving and high efficiency, and easy operation and control. The presence of metal can cause higher hot spot temperature and the generation of transient electron-hole pairs. The electron-hole pairs are easy to adsorb the model compound, and then the model compound and the acid site act, so that the reaction is quickly carried out, and the reaction time is saved.

[0025] (3) The present application uses cheap and renewable activated carbon carrier as a microwave absorber, which can well absorb microwaves and convert them into heat, and also can transfer heat to the sample mixed therewith, so that the reaction can proceed smoothly. At the same time, the raw material of activated carbon is abundant and low in cost, and can be applied to industrial production on a large scale. DETAILED DESCRIPTION

[0026] The specific embodiments of the present application are further described below in combination with the technical solutions.

[0027] Coal-based platform molecules are used as raw materials, isopropyl alcohol is used as a solvent, and activated carbon loaded with nano-metal catalyst is used as a hydrogenolysis catalyst, and its chemical formula is x%Ru-y%Pd / AC. Solid acid is added, the microwave output power is 500-900W, the reaction time is 20-60min in a microwave quartz reaction kettle, and the coal platform molecules are selectively catalytically hydrogenolyzed to prepare phenol and toluene.

[0028] Example 1: Preparation of 3%Ru-2%Pd / AC catalyst

[0029] 5.0g of carrier activated carbon was weighed and immersed in a 100ml beaker containing an aqueous solution containing 0.4054g of RuCl3 and 0.1695g of PdCl2. The obtained sample was dried at room temperature overnight, and then placed in a 100℃ oven for continuous drying for 12h. The dried sample was first treated in a N2 atmosphere to obtain a catalyst precursor; the obtained catalyst precursor was reduced and calcined in a hydrogen atmosphere, the calcination time was 2h, and the reduction temperature was 200℃, to obtain a supported metal catalyst, and the prepared sample was marked as 3%Ru-2%Pd / AC.

[0030] 0.2g of phenyl benzyl ether, 30ml of isopropyl alcohol solvent, 0.1g of the above catalyst and 0.1g of silicotungstic acid solid acid were added to a 100ml quartz reaction kettle and a stirrer was added. Check the airtightness; then introduce the reaction gas 50ml / min H2, set the microwave output power to 800W, the reaction time is set to 30min according to the reaction requirement, and start the reaction. The reaction results are shown in Table 1.

[0031] Example 2-3:

[0032] The conditions are the same as in Example 1, except that the mass ratio of Ru to Pd is adjusted to obtain 5%Ru / AC and 5%Pd / AC in turn.

[0033] Table 1 Effect of different catalyst composition on catalytic activity of phenyl benzyl ether

[0034]

[0035] Note: Others include cyclohexane, cyclohexanol, etc., overall material conservation.

[0036] Reaction conditions for Example 4

[0037] 0.2 g of phenyl benzyl ether, 30 ml of isopropyl alcohol solvent, 0.1 g of 3% Ru-2% Pd / AC catalyst and 0.1 g of silicotungstic acid solid acid were added to a 100 ml quartz reaction tank and a stirrer was added. The airtightness was checked; then the reaction gas 50 ml / min H2was introduced, the microwave output power was set to 800 W, and the reaction time was set to 30 min according to the reaction requirements. After pyrolysis, high-purity nitrogen was continuously introduced until the whole system was cooled to room temperature, the post-reaction product was collected and detected; the product was calculated for yield and component analysis. The reaction results are shown in Table 2.

[0038] Examples 5-8:

[0039] The 3% Ru-2% Pd / AC catalyst prepared in Example 1 was subjected to microwave-assisted catalytic hydrogenolysis performance evaluation at different microwave output powers: a quartz reaction tank was selected, 0.2 g of phenyl benzyl ether, 30 ml of isopropyl alcohol solvent, 0.1 g of catalyst and 0.1 g of silicotungstic acid solid acid were added, and a stirrer was added. The airtightness was checked; then the reaction gas high-purity hydrogen was introduced, the reaction time was set to 30 min, and the microwave output power was set to 500 W, 600 W, 700 W and 900 W, respectively. The specific experimental parameters and reaction yield are shown in Table 2.

[0040] Table 2 Effect of different microwave output powers on catalytic activity

[0041]

[0042]

[0043] Note: Others include cyclohexane, cyclohexanol, etc., overall material conservation.

[0044] Examples 9-12:

[0045] The 3% Ru-2% Pd / AC catalyst prepared in Example 1 was subjected to microwave-assisted catalytic hydrogenolysis performance evaluation at different reaction times: a quartz reaction tank was selected, 0.2 g of phenyl benzyl ether, 30 ml of isopropyl alcohol solvent, 0.1 g of catalyst and 0.1 g of silicotungstic acid solid acid were added, and a stirrer was added. Check the airtightness; then introduce the reaction gas 50 ml / min H2, set the microwave output power to 800 W, and the reaction time is 20 min, 40 min, 50 min and 60 min respectively. The specific experimental parameters and reaction yield are shown in Table 3.

[0046] Table 3 Influence of different reaction times on catalytic activity

[0047]

[0048] Note: Others include cyclohexane, cyclohexanol, etc., overall material conservation.

[0049] Examples 13-15:

[0050] The conditions are the same as in Example 1, except that the amount of silicotungstic acid solid acid is changed, and the amounts are 0.0 g, 0.2 g and 0.3 g respectively. The specific experimental parameters and reaction yield are shown in Table 4.

[0051] Table 4 Influence of different amounts of silicotungstic acid solid acid on catalytic activity

[0052]

[0053] Note: Others include cyclohexane, cyclohexanol, etc., overall material conservation.

[0054] Examples 16-20:

[0055] The 3% Ru-2% Pd / AC catalyst prepared in Example 1 was subjected to microwave-assisted catalytic hydrogenolysis performance evaluation at different substrate concentrations: a quartz reaction tank was selected, the mass of phenyl benzyl ether added was changed (30 ml of isopropyl alcohol), 0.1 g of catalyst and 0.1 g of silicotungstic acid solid acid were added to a 100 ml quartz reaction tank and a stirrer was added. Check the airtightness; then introduce the reaction gas 50 ml / min H2, set the microwave output power to 800 W, and the reaction time is set to 30 min according to the reaction requirements, and the mass of phenyl benzyl ether added is 0.05 g, 0.1 g, 0.3 g, 0.4 g and 0.5 g respectively. The specific experimental parameters and reaction yield are shown in Table 5.

[0056] Table 5 Influence of different amounts of phenyl benzyl ether on catalytic activity

[0057]

[0058] Note: Others include cyclohexane, cyclohexanol, etc., overall material conservation.

[0059] Examples 21-23:

[0060] The 3% Ru-2% Pd / AC catalyst prepared in Example 1 was subjected to performance evaluation for catalyzing different coal-based platform molecules (dibenzyl ether, diphenyl ether, phenoxyethylbenzene, methyl phenethyl ether). In microwave-assisted catalytic hydrogenolysis, 0.1 g of 3% Ru-2% Pd / AC catalyst, 0.2 g of coal-based platform molecules, 30 ml of isopropyl alcohol solvent, 0.1 g of catalyst, and 0.1 g of silicotungstic acid solid acid were added to a stirrer. The air tightness was checked; then 50 ml / min of H2 was introduced as the reaction gas, the microwave output power was set to 800 W, and the reaction time was 30 min. The specific experimental parameters and reaction yields are shown in Table 6.

[0061] Table 6 Influence of different coal-based platform molecules on catalytic activity

[0062]

[0063]

[0064] Note: a Other in the reaction product of dibenzyl ether include methylcyclohexane, cyclohexane, etc., and the overall material conservation.

[0065] b Other in the reaction product of diphenyl ether include cyclohexyl phenyl ether, cyclohexanol, dicyclohexyl ether, etc., and the overall material conservation.

[0066] c Other in the reaction product of phenoxyethylbenzene include cyclohexylethane, cyclohexanol, cyclohexanone, cyclohexane, etc., and the overall material conservation.

[0067] Examples 24-26:

[0068] The 3% Ru-2% Pd / AC catalyst prepared in Example 1 was subjected to performance evaluation for microwave-assisted catalytic hydrogenolysis with different solid acids (phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, silicomolybdic acid). A quartz reaction tank was selected, 0.2 g of phenylbenzyl ether was added (30 ml of isopropyl alcohol), 0.1 g of catalyst and 0.1 g of solid acid were added to the 100 ml quartz reaction tank and a stirrer was added. The air tightness was checked; then 50 ml / min of H2 was introduced as the reaction gas, the microwave output power was set to 800 W, and the reaction time was set to 30 min according to the reaction requirements. The specific experimental parameters and reaction yields are shown in Table 7.

[0069] Table 7 Influence of different coal-based platform molecules on catalytic activity of phenylbenzyl ether

[0070]

[0071] Note: Other includes cyclohexane, cyclohexanol, etc., overall material balance.

[0072] Obviously, the above-mentioned embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or variations can also be made by those skilled in the art. Here, it is not necessary and also impossible to enumerate all the implementation modes. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for breaking CO bridging bonds in coal-based platform molecules via microwave-assisted catalytic hydrogenolysis, characterized in that, The steps are as follows: Using coal-based platform molecules as raw materials, wherein the coal-based platform molecules are one of phenyl benzyl ether, dibenzyl ether, diphenyl ether, and phenoxyethylbenzene, isopropanol is used as solvent, and Ru-Pd / AC catalyst is used as hydrogenolysis catalyst. The Ru-Pd / AC catalyst has a Ru loading of 0 wt%~5 wt% and a Pd loading of 0 wt%~5 wt%, wherein the Ru loading and Pd loading are not both 0 wt%. Solid acid is added, and hydrogen gas is introduced and the flow rate is controlled at 50 ml / min. The microwave output power is set to 500-900 W, and the reaction time is 20-60 min. In the microwave reactor, the CO bridging bonds in the coal platform molecules are selectively hydrogenated to generate aromatic compounds and phenol. The solid acid is one of phosphotungstic acid, silicotungstic acid, phosphotomolybdic acid, and silicotomolybdic acid, and its mass ratio with the Ru-Pd / AC catalyst is no greater than 3.

2. The method for breaking CO bridging bonds in coal-based platform molecules via microwave-assisted catalytic hydrogenolysis according to claim 1, characterized in that, The mass ratio of Ru-Pd / AC catalyst to coal-based platform molecules is 1:1 to 1:

10.

3. The method for breaking CO bridging bonds in coal-based platform molecules using microwave-assisted catalytic hydrogenolysis according to claim 1, characterized in that, The aromatic compounds mentioned are toluene and ethylbenzene.

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